Treatment of hydrocarbon gases



Patented May 5, 1936 UNITED STATES PATENT OFFICE TREATMENT OFHYDROCARBON GASES Jacque C. Morrell, Chicago, 111., assignor toUniversal Oil Products Company, corporation of Delaware Chicago, 111., a

No Drawing. Application January 19, 1933. Serial No. 652,575

7 Claims.

- used as constituents of gasoline so that the overall yield of motorfuel from the cracking process may be treated directly or after removalof the hydrogen sulfide contained therein. The gases to be treated bythe process may also be produced by subjecting natural or otherhydrocarbon gases to elevated temperatures and pressures to crack themand increase their content of unsaturated hydrocarbons.

In cracking heavy hydrocarbon oils to produce lower boiling fractions,the yield of gasoline is limited by the fact that as more severeconditions particularly of temperature and time are imposed, the gas andcoke yields increase out of proportion to the yield of gasoline and apoint may be reached where the gasoline yield actually decreases whilethat of the less desirable products, gas and coke, sharply increases.Apart from their use as fuel, the gases resulting from crackingoperations have heretofore been looked upon as an undesirable by-productso that a process for increasing the yield of desired gasoline fractionsand at the same time decreasing the yield of gas will have economicvalue.

In one specific embodiment the present invention comprises the treatmentof gases from cracking plants with solutions of zinc chloride alone orin combination with halogen acids such as hydrogen chloride tocontrollably produce polymers from the olefins in the gases, suchpolymers being of a character suitable for use as con-v stituents ofgasoline and of particular value in improving its anti-knock value.

The composition of the gases from cracking processes varies over wideranges in respect to paraflins and olefins and sulfur derivatives ofhydrocarbons, the composition depending upon the type of charging stockcracked and the severity of cracking conditions. The following analysisis typical of the gases produced in the cracking of heavy distillatesand residues in present day commercial plants:

Per cent Hydrogen 12 Methane Ethan Ethylene Propane Propylene ButanesButylenes Pentanes Amylenes Miscl. heavier hydrocarbons The olefins,however, may run as high as 40% and over as a result of intensivecracking operations at high temperatures for the production of arcmaticsor high anti-knock gasolines and even higher if oils are cracked withthe primary object of gas production. The latter type of gases mayproduce the higher yields of desirable liquid products.

Olefin-containing gases may be subjected to the action of zinc chloridesolutions according to the process of the invention in a number of ways;The simplest method of operation consists in bubbling the gases througha stationary pool of zinc chloride solution, the concentration of whichis varied to produce the desired rate and character of polymerization.In this method of operation liquid hydrddarbon polymers will accumulateon the surface of the aqueous solution and some may be carried on inunaffected residual gases to be later recovered by absorption.

Another alternative method of operation consists in passing the gasstream upwardly countercurrent'to descending solutions of zinc chloride,the stream being subdivided by passage over relatively inert spacingmaterial such as Raschig rings, crushed firebrick, silica fragments,fullers earth, clays, etcetera, or towers containing regularly spacedtrays of the perforated or bubble type may be employed.

A still further alternative mode of operation, which may be operated inconjunction with the two mentioned above may consist in atomizing Cit Inall cases of treatment it is comprised within the scope of the inventionto re-use the chloride solutions insofar as their polymerizingeffectiveness may indicate. If the solution becomes contaminated withpartly soluble polymers or addition compounds with the zinc chloride itmay be subjected to any suitable regenerating steps to bring it back toa condition for use.

It is to be understood, of course, that the gases to be treated mayoriginate or be led directly from a concurrently operating crackingprocess.

Obviously, no entirely general rules can be laid down for obtaining thebest results with all gases, not only because of the variations in thepercentage of olefins which they contain, but also on account ofvariations in the types of olefins as to whether they are normal or isocompounds and because 01' the variation in the relative propor-' tionsof these different types. However, a consideration of the generalmechanism of the reactions furnishes some guidance for predeterminingthe best conditions of operation in any case though the exactdetermination of conditions is usually a matter of trial.

As exemplifying the type of reaction which results in the formation ofsimple polymers from a mono-olefin, the case of isobutylene may beconsidered. When isobutylene is treated with a concentrated'zincchloride solution in a relatively large volume, say by weight of theisobutylene, varying percentages of di-, triand tetrabutylene areformed. There is evidence to support the assumption that hydrochloricacid resulting from partial hydrolysis of the zinc chloride addsdirectly to isobutylene to form a butyl chloride which then reacts withfurther amounts of iso-butylene to form an octyl chloride as anintermediate product, this then decomposing with loss of hydrochloricacid to form octylene, and allowing the hydrochloric acid to reactfurther in the same cycle. There is evidence also in support of the viewthat intermediate addition compounds are formed between olefins and zincchloride, a compound of this character having the formula CsHio.2ZnCl2,being formed by the direct addition of one molecule of amylene to two ofzinc chloride. Such compounds are readily decomposed by water, which mayaccount for the observed fact that a certain concentration of solutionis desirable to insure the desired polymerization reactions. Whateverthe exact course of the reactions may be it is nevertheless an observedfact that liquid products boiling within gasoline range and possessingunusually high anti-knock value can be produced from the olefins incracked gases by the use of zinc chloride solutions of regulatedstrength which are contacted with the gases in any suitable manner.

While elevated temperatures are sometimes desirable, the temperatureused must not be high enough to cause too extensive polymerization. Insome cases it suffices to merely pass the fixed gases from an oilcracking process through a stationary pool of concentrated zinc chloridesolution, at ordinary temperatures and pressures. In other cases,elevated temperatures and pressures are desirable, particularly if thepercentage of readily polymerizable olefins is relatively low.

Control of the extent and action 01 the p ymerizing reactions may be tosome extent a matter of adjustment of the amount of moisture andhydrochloric acid present. In the operation of the process moisthydrochloric acid or hydrogen chloride may be injected into the streamof gases, or either hydrochloric acid or water may be introduced intotreating equipment so that aqueous hydrochloric acid is present as aliquid phase, or hydrochloric acidmay be a constituent of thepolymerizing salt solution in any desired quantity.

An example of results obtainable by the use of the process may be givenin connection with a gas having the composition shown in the precedingtable. This gas, produced at a rate of 1,000 cubic feet per barrel ofcharging oil to a cracking plant may be passed at atmospherictemperature and pressure upwardly countercurrent to a solution of zincchloride of approximately 80 to 85% concentration. The gas mixture maybe saturated with water vapor and contain in addition a small percentageof hydrochloric acid gas, say, about 0.3% by volume of the gas mixture.

By this operation there may be recovered from two to two and one-halfgallons of 51 A. P. I. gravity liquid boiling within the range of 120 to410 F. and consisting for the most part of hexylenes. octylenes anddecylenes and some higher homologs, resulting from the formation ofdimers from the corresponding olefins of one-half their molecularweight. The resulting liquid product may have an octane number oranti-knock value exceeding that of benzol. In the case under discussionthe gasoline yield from oil charged to the cracking plant may beincreased from a total of 60 to 65% by the incorporation of thesepolymers with the gasoline normally produced. Furthermore, owing to thehigh anti-lmock value of the polymers the octane number of the gasolinemay be increased from '75 to 80, which constitutes a further advantage.Good results may be obtained with zinc chloride in aqueous solution atan elevated temperature of approximately 400 F. and a pressure of 400pounds per square inch. Under these conditions employing a gas from acracking process containing 35% of olefins, approximately three gallonsof liquid product of high anti-knock value may be obtained per thousandcubic feet of gas. The anti-knock value of the liquid thus obtainedfrequently exceeds that of benzene and is highly desirable as a motorfuel blending agent.

The examples given herein are merely illustrative of the manypossibilities of the process and are not to be considered as limitationsthereof.

I claim as my invention:

1. A process for the treatment of oleflnic gases to polymerize thegaseous olefin hydrocarbons and. convert the same into liquidhydrocarbons, which comprises subjecting the said gases in the absenceof any substantial quantity of normally condensible hydrocarbon vaporsto the action of a concentrated aqueous solution of zinc chloride at atemperature and pressure such that the zinc chloride is in aqueoussolution during the polymerization of the olefins.

2. A process for the treatment of olefinic gases to polymerize thegaseous olefin hydrocarbons and convert the same into liquidhydrocarbons, which comprises subjecting the said gases in the absenceof any substantial quantity of normally condensible hydrocarbon vaporsand while in heated condition to the action of an aqueous solution ofzincchloride at a temperature and pressure such that the zinc chlorideis in aqueous solution during the polymerization of the olefins.

3. A process for the treatment of olefinic gases 30 Y substantialquantity of normally condensible hy- 4. A process for the treatment ofgaseous hydrocarbons from a cracking process to polymerize the olefinhydrocarbons contained therein for the purpose of producing liquidhydrocarbons suitable for high anti-knock motor fuel or a blending agenttherefor, which comprises subjecting the said gases in the absence ofany substantial quantity of normally condensible hydrocarbon vapors andwhile in heated condition to the action of an aqueous solution of zinc'chloride at a temperature and pressure such that the zinc chloride isin aqueous solution during the polymerization of the oleflns.

5. A process for the treatment of gaseous hydrocarbons from a crackingprocess to polymerize the olefin hydrocarbons contained therein for thepurpose of producing liquid hydrocarbons suitable for high anti-knockmotor fuel or a blending agent therefor, which comprises subjectingthesaid gases in the absence of any carbon vapors and while in heatedcondition under superatmospheric pressure to the action drocarbon vaporsand while in heated condition under superatmospheric pressure to theaction of an aqueous solution of zinc chloride at a temperature andpressure such that the zinc chloride is in aqueous solution during thepolymerization of the'olefins.

6. A process for the treatment of gaseous hydrocarbons from a crackingprocess to polymerize the oleiln hydrocarbons contained therein for thepurpose of producing liquid hydrocarbons suitable for high anti-knockmotor fuel or a blending agent therefor, which comprises subjecting thesaid gases in the absence of any substantial quantity of normallycondensible hydroot a concentrated aqueous solution of zinc chloride ata temperature and pressure such that the zinc chloride is in aqueoussolution during the polymerization of the oleflns.

7. A process for the treatment of oleflnic gases to polymerize thegaseous olefln hydrocarbons and convert the same into liquidhydrocarbons, which comprises subjecting the said gases in the absence'of any substantial'quantity of normally con-

